There are two applications where electronic binoculars are particularly useful: in low-light level viewing and infrared imaging systems. In the former case, the sensor uses an image intensifier that is imbedded in the design. In the latter case, the sensor detects wavelengths that lie outside the human spectral response.
Generally in electronic imaging systems there are a limited number of pixels in the sensor and the display, so one has to balance the image quality vs. the field of view (FOV). An example of this trade off is using a 600.times.600-pixel display and matching the display to the maximum resolution of the eye, which is 1 arc minute. In this configuration the maximum full field of view is about 20.degree..times.20.degree.. Conventionally if one wants to increase this field of view, the cost will come in the form of a decrease in image quality as limited pixels are distributed over a larger field of view. Alternatively, one can increase the number of pixels in the display, but with a cost penalty.
Recently researchers have begun to investigate the potential usefulness of variable addressibility systems. Much of this research has been in the areas of robot vision and virtual reality. In both cases there is a desire to increase the field of view, using the eye as a generic model. There are three primary methods used to obtain foveated information, log-polar mapping [F. L. Lim et al. (1996) Proceedings of the 13.sup.th International Conference on Pattern Recognition 1, 795-799; Konstantinos Daniilidis (1995) Computer Analysis of Images and Patterns, 6.sup.th International Conference, CAIP '95, 82-89], varying the size of CCD elements [G. Kreider and J. Van der Speigel (1990) Proceedings of the SPIE, Vol. 1242 Charge-Coupled Devices and Solid State Optical Sensors 133-140; I. Debusschere et al. (1990) Sensors and Actuators 456-460] and creating special high distortion lenses.
In the virtual reality community, generally the trend is going towards using four displays for each head mounted application [Eric Howlett (1992) Proceedings of SPIE, Vol. 1669 Stereoscopic Displays and Applications III 193-203; Eric Howlett (1990) Proceedings of SPIE, Vol. 1256 Stereoscopic Displays and Applications 210-222]. Two displays are used with a high distorting lens to give a large FOV while the other two are used for high-resolution inserts. Similar techniques are being tested for helmet mounted displays used in flight simulators [George Kelly et al. (1992) Proceedings of SPIE, Vol. 1695 Helmet-Mounted Displays III 58-63; Paul Wetzel et al. (1990) Proceedings of SPIE, Vol. 1289, Cockpit Displays and Visual Simulation 163-167]. The drawback of this technique comes in the form of size, weight, cost and complexity.
In the robot vision research areas, special fish-eye lenses have been designed that vary the resolution as a function of field [Yoshikazu Suematsu and Toshiyuki Hayase (1990) 16.sup.th Annual Conference of IEEE Industrial Electronics Society 1343, 581-585; N. Alvertos and E. L. Hall (1984) Proceedings of the SPIE--The International Society for Optical Engineering 449, pt. 1, 230-239; Shishir Shah and J. K. Aggarwal (1996) Pattern Recognition 29, No. 11, 1775-1788]. A couple of studies have also attempted to match their distortion curves with the visual acuity curve of the human eye [Sohto Shimaizu et al. (1996) 22.sup.nd International Conference on Industrial Electronics, Control, and Instrumentation 1600-1605; Y. Kuniyoshi et al. (1995) Recent Developments in Computer Vision, Second Asian Conference on Computer Vision, ACCV '95 191-200]. None of these have been designed to interface with a human.
There has been one previous attempt to use the variable acuity concept to increase the FOV in a night vision goggle application [Wayne Schoenmakers and Benjamin Roland (1991) "Variable Acuity Optics Study," Summary Final Technical Report under Contract DAAB07-87-C-F059 to Hughes Corp.]. A prototype was developed, but the project eventually ended with several unsolved problems. The system was too heavy and bulky for their specific application. It also required several aspheric surfaces, which are expensive to fabricate. These problems were compounded with subjective human factor concerns. Testing personnel noted a disturbing visual effect when viewing through the system. Although the testers did not see any classical optical distortion (straight lines exhibiting the tendency to curve) they did have the feeling that something was amiss off-axis. The poor off-axis resolution distracted the viewer. This made it difficult to concentrate on viewing the on-axis image. There was no known basic engineering explanation for the perceived low resolution.